The universal claim I'm disproving is that peak visible resolution always occurs at the same aperture.

So you think that the human eye will always perceive a resolution difference when stopping down to any aperture, using any resolution of sensor to capture the image?

No-one disputes that the maximum is always at the same aperture. That has repeatedly been said. I'm talking about whether in the real world you will notice any difference and whether you can then actually stop down further than the peak without incurring any perceived loss of resolution.

You will not notice much difference if you open up more, either. All this based on you idea that a 5% drop from, say, 1200 is the same, visually, as 5% drop from 2400, which is a very bold assumption and flat out wrong at moderate viewing sizes.